Political Brokers: Partisans or Agents? Evidence from the Mexican Teachers’ Union Horacio Larreguy Harvard University Cesar E. Montiel Olea Columbia University Pablo Querubin New York University Abstract: Political brokers mobilize voters all over the world, yet little is known about what motivates them to do so. This article theorizes about two drivers of brokers’ efforts: (1) incentives—monetary rewards or sanctions—and monitoring and (2) partisan attachment. We examine our theory using data on the Mexican National Educational Workers Union (SNTE), Latin America’s largest union and a well-known political machine. Consistent with the role of teachers as brokers, we find that the vote share of parties supported by the SNTE machine is higher in polling stations located in schools. This effect is absent when teachers are asked to mobilize voters in support of a party for which they have no partisan attachment, and it is uncorrelated with the union’s monitoring capacity. This suggests that partisan attachment, rather than incentives and monitoring, explains the SNTE’s effectiveness as a political machine. Replication Materials: The data, code, and any additional materials required to replicate all analyses in this arti- cle are available on the American Journal of Political Science Dataverse within the Harvard Dataverse Network, at: https://doi.org/10.7910/DVN/BFLPBK. I n many developing countries, politicians and polit- ical parties rely on political brokers as crucial inter- mediaries between themselves and voters. Brokers are responsible for mobilizing voters through clientelis- tic and vote-buying strategies that are critical to electoral success. However, while recent work has documented the electoral impact of brokers (Cant ´ u 2016; Larreguy 2012; Larreguy, Marshall, and Querubin 2016; Rueda 2015), as well as the different strategies they pursue to mobi- lize voters (e.g., see Auyero 2000; Diaz-Cayeros, Estevez, and Magaloni 2016; Mares and Young 2016), we have lit- tle understanding of the drivers of brokers’ efforts. This limits our ability to comprehend the politics of contexts in which clientelism plays an important role in shaping electoral outcomes. Horacio Larreguy is Associate Professor, Department of Government, Harvard University, 1737 Cambridge Street, Room 408, Cambridge, MA 02138 (hlarreguy@fas.harvard.edu). Cesar E. Montiel Olea, Institute for Social and Economic Research and Policy, Columbia University, 420 W. 118th Street, Suite 370, New York, NY 10027 (cm3382@columbia.edu). Pablo Querubin is Assistant Professor, Department of Politics, New York University, 19 W. 4th Street, Room 428, New York, NY 10012 (pablo.querubin@nyu.edu). This article benefited from helpful conversations and suggestions from the editor, two anonymous referees, Christopher Chambers-Ju, Cesi Cruz, Jorge Dominguez, Andrei Gomberg, Guy Grossman, Emilio Gutierrez, Daniel Hidalgo, Nahomi Ichino, Steve Levitsky, Gwyneth McClendon, Marco Morales, Vicky Murillo, Dan Posner, Cyrus Saami, Jake Shapiro, James M. Snyder, and Lauren Young. Participants at the APSA 2015, Columbia SSDS Seminar, Harvard Positive Political Economy Seminar, MIT Political Economy Workshop, MPSA 2014, NEUDC 2013, and NEWEPS 2014 conferences provided essential feedback. We are greatly indebted to Elisa Lavore and Lucrecia Santiba˜ nez, who helped us with the data on the dissident local school sections. We also thank an anonymous informant, closely acquainted with Elba Esther Gordillo, who provided us with very valuable information that deeply informed our study. Alejandra Menchaca provided support and patience throughout the project. This article theorizes that there are two main drivers of brokers’ efforts. First, parties often incentivize bro- kers with pecuniary rewards or sanctions that are con- ditional on brokers’ observed mobilization efforts. The party–broker relationship is often subject to moral hazard: Whenever brokers’ electoral interests are not nec- essarily aligned with those of the party, brokers will have an incentive to shirk. Thus, parties must be able to mon- itor their brokers’ mobilization performance in order to enforce their efforts, and either withhold rewards from or impose costly sanctions on brokers who shirk or reward those who effectively mobilize voters. This is particularly relevant, for example, in contexts with hired political bro- kers (Larreguy 2012; Larreguy, Marshall, and Querubin 2016) who, absent any monitoring, would exert little or no effort in mobilizing voters. American Journal of Political Science, Vol. 61, No. 4, October 2017, Pp. 877–891 C  2017, Midwest Political Science Association DOI: 10.1111/ajps.12322 877